1. Field of the Invention
The present invention relates to an amorphous dielectric thin film for use in a capacitor of a highly integrated memory device and a manufacturing method thereof. More particularly, the present invention relates to an amorphous dielectric thin film that includes a bismuth (Bi)-titanium (Ti)-silicon (Si)-oxide (O) (BTSO)-based material having an amorphous microscopic structure as a capacitor of a memory device, and a manufacturing method thereof.
2. Description of the Related Art
As predicted by Moore's Law, the packing density of dynamic random access memory (DRAM), i.e., a highly integrated memory device, nearly quadruples every three years and design rules are continuously decreasing. Thus, a planar space occupied by a unit cell continuously decreases. In particular, in a case of a DRAM consisting of a single transistor and a single capacitor, the planar space of the capacitor is necessarily decreased, which in turn reduces the planar dimension of the capacitor, thereby lowering the capacitance C of the capacitor in accordance with equation 1 below:
                    C        =                  ɛ          ⁢                                          ⁢                      A            t                                              (        1        )            where ∈ denotes a dielectric constant, A denotes an effective area of the capacitor, and t denotes a thickness of the dielectric film.
Accordingly, although a feature size of a device continuously decreases, a capacitance (>25 fF/cell) required for the DRAM device operation should be maintained. Therefore, research continues into decreasing a thickness of a dielectric thin film and increasing an area of the dielectric film. Recently, considerable effort has been devoted to using a high dielectric oxide layer with a high dielectric constant (high-k) in place of a material such as SiO2, which is used to form a conventional dielectric thin film.
In the semiconductor industry, a high dielectric thin film is employed in a gate oxide layer and a dielectric film of a DRAM capacitor. In the case of the gate oxide layer, current research is directed toward an oxide layer based on Hf or Zr and a group III metal oxide layer such as Lanthanide. Generally, because of a narrow energy band-gap, the high dielectric gate oxide layer suffers from a large leakage current and degraded thermo-stability at a high temperature during bonding to a silicon surface. Accordingly, attempts have been made to remedy these disadvantages of the dielectric films by adding SiO2 or Al2O3 with excellent thermo-stability and a large energy band-gap.
However, a thin film formed by mixing a high dielectric material with SiO2 or Al2O3 disadvantageously has an amorphous microscopic structure and a significantly lower dielectric constant. Resultantly, the use of such an amorphously structured mixture as a capacitor dielectric material is not attractive. For example, the dielectric constant of a (Ba,Sr)TiO3 thin film (BST), which is known to be 250 or higher in a crystalline thin film with a perovskite structure, is decreased to approximately 25 when the thin film is changed to have an amorphous microscopic structure.
In order to be used as a capacitor dielectric material of a Gigabit-grade DRAM, a physical thickness tphy of a thin film should be less than 15 nm and an equivalent oxide layer thickness toxeq should be roughly less than 1 nm. Therefore, such a conventional amorphous dielectric thin film could not be used. Accordingly, research on the capacitor dielectric film concentrated on a crystalline high dielectric thin film that has a problem of increased leakage current through a grain boundary once the thickness thereof becomes reduced to approximately 15 nm.
Further, the most serious problem occurring when applying a poly-atomic dielectric material such as BST is a difficulty in depositing a thin film with consistent composition in the case of a three-dimensionally structured pattern during the manufacture of a three-dimensional capacitor. This problem is caused by a small charge-to-radius ratio of a group II alkaline earth metals such as Ba and Sr, which results in an unstable precursor structure and insufficient vapor pressure.